The assignee of this invention has manufactured and sold toner cartridges of two different general designs. For its larger laser printers, the cartridge has contained a pump to meter toner of the kind disclosed in U.S. Pat. Nos. 5,012,289 to Aldrich et al. and 5,101,237 to Molloy, while the external structure of the cartridge is as disclosed in U.S. Pat. No. 5,136,333 to Craft et al. Details of other elements in the cartridge have varied.
For its smaller laser printers, the cartridge is as disclosed in U.S. Pat. No. 5,337,032 to Baker et al., which has a toner hopper extending well below a level having the toner adder roller and which has independent driven systems for the photoconductor roller and for the developer roller system as disclosed in U.S. Pat. No. 5,331,378 to Baker et al.
Further improvements to these cartridges have involved, inter alia, a hopper exit agitator, such as is shown and described in U.S. Pat. No. 5,875,378 to Campbell et al.
To meter the toner that is used to create the electrophotographic image in these smaller laser printers, a doctor blade is positioned to contact the developer roller and create a nip therebetween. The toner is delivered to the doctoring nip for placement on the developer roller. The doctor blade controls the amount of toner that reaches the developer roller by allowing only a thin layer of toner particles through the doctoring nip.
It can be appreciated by those skilled in the art that, in this operation, the toner tends to accumulate behind the doctor blade. The toner becomes packed, interfering with the intended flow thereof to the developer roller. This leads to starvation at the doctoring nip. Furthermore, the packed toner can become fused to the working surface of the doctor blade due to heat and/or pressure caused by the heavy packing of the toner itself. The ultimate result is the emergence of problems with print quality.
There is thus identified a need of preventing the accumulation of toner behind the doctor blade.